On Friday, Antônio José Pita Martins became the third worker to die while working in or near the ground, a tally that accounts for half the fatalities during construction of the 12 stadiums for June's finals.

The 55-year-old died after being struck on the head by a piece of falling iron as a crane that had been used to build the stadium's roof was dismantled outside the arena in northern Brazil.

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A hospital statement later said that a combination of head and chest injuries had caused Martins' death.

"With great sadness we send our sincere condolences to the family, on behalf of both FIFA and the Local Organising Committee," wrote FIFA Secretary General Jérôme Valcke on Twitter.

Work at the Arena da Amazonia, which football's world governing body FIFA had wanted to be finished in December, is one of several stadiums in Brazil running behind schedule - with just 125 days to go before the tournament begins.

In December, Marcleudo de Melo Ferreira died after falling nearly 35 meters from the roof of the stadium.

The 22-year-old's death, which followed Manaus' first fatality in March 2013, prompted his fellow construction workers to go on strike until they received assurances of improved safety conditions.

These appear to still be in some doubt following the death of Martins, a Portuguese national.

A statement was released by Brazil's Sports Minister Aldo Rebelo expressing regret for the death.

"The Sports Ministry laments the death of worker Antônio José Pita Martins, victim of an accident at the construction site of the Arena da Amazonia, on Friday, in Manaus," he said.

"Personally and in the name of the federal government, I express deep regret and express my feelings and solidarity with the family and friends of the worker."

It is wording with which Rebelo is becoming depressingly familiar, having released a nearly identical statement in the wake of Ferreira's death.

Two other workers were killed last November in Sao Paulo, following the collapse of a crane at the stadium set to host the opening game of the finals on June 12, while another died in Brasilia.

The Manaus stadium will also stage the following matches: United States-Portugal, Cameroon-Croatia and Honduras-Switzerland.

News of the death came a day after fierce clashes between police and citizens of Rio de Janeiro as the latter protested over increased public transport costs.

Many Brazilians are unhappy about the huge governmental spending on the World Cup when they say such public services as schools, hospitals and infrastructure are in desperate need of repair.